“Can you explain what makes confession of sin the key that opens the door to being spiritual”?

This believer probably does not realize the importance of this question to her spiritual growth. This is the type of question a spiritually mature believer seeks to have answered that excites me as a pastor-teacher.

The answer will require being able to put milk doctrines with meat doctrines to spiritually advance you in epignosis(a more exact or fuller knowledge that powerfully influences you as a believer in the Grace Gospel of Jesus Christ.